1. Field of the Invention
This invention relates to the field of Digital Versatile Disks, or DVD. More particularly, the present invention relates to methods and apparatuses for reducing the data access time from a digital storage medium, such as a DVD Read Only Memory (hereafter, DVD-ROM) or a recordable DVD (hereafter referred to generically as DVD-Random Access Memory or DVD-RAM).
2. Description of the Related Art
A sector in a DVD is variously called a data sector, a recording sector or a physical sector, depending upon its configuration. FIG. 1 shows a data sector of a DVD disk. As shown in FIG. 1, a data sector includes 2048 bits of data, 4 bytes of identification (ID) data; 2 bytes of ID Error Detection code (IED), 6 bytes of Copyright Management Information (CPR MAI) and 4 bytes of Error Detection Code (EDC). The 2048 bytes of data are then scrambled, using a feedback shift register. An ECC block is made up of 16 of the data sectors shown in FIG. 1. The 16 data sectors of the ECC block are then encoded, using Cross-Interleaved Reed-Solomon Code (CIRSC). An ECC block, including outer code parity (PO) and inner code parity (PI), is shown in FIG. 2. As shown in FIG. 2, 10 bytes of PI are added after each row, and one row of 182 bytes of PO are added after each of the 16 data sector of the ECC block, for a total of 16 rows of 182 bytes of PO data.
A recording sector is formed by interleaving the PO data in each of the 16 data sectors. One such recording sector is shown in FIG. 3. Each recording sector, therefore, includes a data sector consisting of 12 rows of 172 bites, each row having 10 bytes of PI data appended thereto. One row of 182 bytes of PO data is also included, as a result of the interleaving process referred to above.
Finally, a physical sector, according to the DVD specification, is formed by a two step process. First, an 8:16 modulation conversion is carried out, which effectively doubles the width of each sector. Then, 32 bits of frame synchronization information are prepended to each of the recording sectors in each row. A physical sector is shown in FIG. 4. As shown therein, each Sync Frame includes 4 bytes of synchronization information, each indicating the start of a recording sector, each recording sector consisting of 1456 bits, or 172 bytes of data and 10 bytes of PI information. Each synchronization code (hereafter"sync pattern" ) SYN0 to SYN7 is selected according to sync tables, not shown.
To access (e.g., to read or write) data from a DVD-ROM or DVD-RAM, a DVD read or read/write device must find the beginning of each physical sector. As shown in FIG. 4, only a single SYN0 bit pattern is included in each physical sector. To find the beginning of a physical sector, therefore, requires the DVD device to find the SYN0 bit pattern. It however, the disk has been somehow damaged or random noise has prevented the device from identifying the SYN0 pattern, the DVD-ROM/RAM device may be unable to locate the SYN0 bit pattern and thus will not be able to identify the beginning of a physical sector. The DVD device must then backtrack and attempt to read the physical sector again, by again attempting to detect the singular SYN0 bit pattern marking the beginning of each physical sector. This procedure may be repeated for a predetermined number of attempts before the SYN0 bit pattern is detected. Each time, the DVD-ROM/RAM device must traverse all 38,688 channel bits of the physical sector before backtracking to attempt detection of the SYN0 pattern again. This repeated traversal of the physical sector and repeated scan for the unique and singular SYN0 pattern necessarily increases the data access time of such DVD ROM/RAM devices. Moreover, if the disk is damaged and the SYN0 bit pattern is unreadable, the physical sector including the damaged SYN0 pattern will be unreadable, potentially rendering the data or program stored on the DVD-RAM or ROM inaccessible and the disk useless.
What are needed, therefore, are devices and methods to reduce the access time of data from DVD-ROM and DVD-RAM disks. What are also needed are devices and methods to reduce the data access time of DVD-ROM and DVD-RAM disks, as well as methods and devices that are tolerant of some manufacturing defects and/or to the effects random noise, particularly in the disk areas reserved for the physical sector synchronization patterns.